Behavioral development of the Norway rat is analyzed from a novel perspective in which behavioral and physiological exchanges between mother and offspring serve as ontogenetic mechanisms that coordinate parent-offspring relations, and establish perceptual preferences in both parent and young that guide the expression and development of behavior. Thermotactile stimulation is analyzed as a component of their contact interactions, and the behavioral and physiological effects of conductive and convective heat exchanges are evaluated empirically. Thermal energy is studied as a "primary metabolic commodity" that has regulatory effects on parent and offspring and which may serve to establish learned associations with other cues. Behavioral observations of mother-litter interactions are used to establish quantitative assessments of body surface area for heat transfer, and direct measures of thermal flux are made. The consequences of these exchanges on the development of olfactory and filial preferences are studied. Changes in salt appetite associated with the maternal condition are analyzed in terms of perceptual changes and a consequence of specific influences of the offspring on the dam. The control of maternal perception and maternal behavior are analyzed in the context of resource exchange and offspring control. Chemical analyses of pup urine will be made for preliminary isolation of a gender-specific factor that regulates maternal licking of young. Modification of reciprocal exchanges are used to define transitions in the parent-offspring relationship. Comparative studies with Peromyscus californicus, a species that displays bi-parental care are used to test a mutualistic model of parental behavior. New studies of energetic controls of weaning are proposed for the Norway rat.